Temporal food web variability in an upper Missouri River backwater: energy origination points and transfer mechanisms

Abstract – Energy transfer mechanisms often cannot be identified with either an isotope or a food habits analysis; however, a combined assessment provided collaborative support for depicting backwater food webs. Lateral dimensions in riverine function substantially influence backwater ecology; however, backwater communities are highly dynamic and infrequently investigated due to logistical difficulties. We created seasonal food webs for an upper Missouri River backwater using a combined food habits and stable isotope analysis. Temporal transition of energy origins was apparent. In the spring, carbon primarily originated from sediments, detritus and periphyton. During mid-summer, carbon was derived from a variety of sources, but included large proportions of terrestrial plants and particulate organic matter. By early fall, the backwater was uncoupled from the river, and autochthonous phytoplankton appeared to be the dominant carbon source. During all sample periods, Chironomidae was an important trophic link conveying energy from the primary producers to the higher consumers. Additionally, zooplankton were an important energy transfer taxa to the abundant age-0 fish community in the fall, and Corixidae were important in the spring.